This invention relates generally to lamps for use with motor vehicles, and more particularly to vehicle lamps having an array of light emitting diodes (LEDs) to provide both clearance and side marker functions.
The Society of Automotive Engineers (SAE), in SAE standard J592 JUN92, defines a clearance lamp as a lamp mounted on a vehicle to provide light to the front or rear to indicate the overall width and height of the vehicle. A side marker lamp is defined as a lamp mounted on a vehicle to provide light to the side to indicate the overall length of the vehicle. Finally, a combination clearance and side marker lamp, designated by the code "PC", is defined as a lamp simultaneously fulfilling the requirements of both clearance and side marker lamps. Typically, clearance, side marker lamps and PC lamps used on automobiles and truck/trailer combinations use standard high-intensity incandescent bulbs as a light source with an optical lens in front of the light source to provide a desired photometric pattern. The lens usually provides an important second function of protecting the light source from dirt, moisture and other foreign matter. Incandescent light sources, however, have a relatively short life and may further be somewhat delicate in that excessive handling may result in failure due to filament breakage.
LEDs are useful in vehicle lamps such as for combination brake, turn and tail lamps, and for clearance or side marker lamps. An advantage of using LEDs is that they have an operating life of up to 100,000 hours before they begin to degrade.
Ordinarily, LEDs are not used in PC lamps due to the difficulty in designing lens optics to spread the light, emitted by an LED in a narrow cone pattern, into an arc pattern of up to 180 degrees. Moreover, providing a PC lamp with LEDs would require multiple LEDs in order to satisfy the Federal Motor Vehicle Safety Standard (FMVSS) 108 lighting requirements. Using multiple LEDs in a single lamp housing thus further creates heat dissipation concerns since it is known that high LED junction temperatures can significantly reduce LED light output. What is therefore needed is a PC lamp assembly that uses a robust light source having a long lifetime, and that sufficiently dissipates heat so as not to degrade the light source.